For the first time in a non- emergency situation, the city is closing traffic on the northbound Jones Falls Expressway during church-going hours Sunday for a festival designed to draw pedestrians, bikers and roller bladers to use the highway to enjoy the little-known waterway below.

The city's deputy director of Public Works, Dave Montgomery, said yesterday the decision to close a three-mile stretch of Interstate 83 -- the key artery connecting downtown and North Baltimore -- from 8 a.m. to noon Sunday was reached after a careful study of traffic patterns.

"There's very little [northbound] traffic volume on Sundays. We looked long and hard at it for four months," Montgomery said, adding that he doubts the closure will adversely affect traffic and the surrounding communities.

Drivers will be advised to take Charles or Calvert streets.

It is not clear how the closure will affect church-bound drivers. The Rev. Constantin Monios of the downtown Greek Orthodox Church said the city took church commuters into consideration and that most church services do not end until after noon. He compared the event to the annual walk across the Bay Bridge.

Closing part of the JFX to vehicle traffic is a worthwhile way to support the environmental restoration of the Jones Falls as a "linear park," city officials said.

U.S. Rep. Benjamin L. Cardin, a Maryland Democrat, will take part in the Jones Falls Celebration, which starts on Saturday at 4 p.m. with a free Caribbean music concert under the Wyman Park Drive bridge and continues through Sunday.

At the festival, the result of teamwork by several Baltimore nonprofits, Cardin will announce the recent selection of Baltimore to receive $1.3 million in federal transportation funds to begin building a "greenway" trail system along the Jones Falls.

"Baltimore will be part of a national demonstration program of urban greenways," said Cardin. He said the first phase of the 10-foot-wide asphalt trail, which will open next year, will link Penn Station and Druid Hill Park.

In five to 10 years, Cardin said, the trail will go from the Inner Harbor to Lake Roland in North Baltimore. "There are lots of treasures and secrets by the falls," said Cardin. "This [greenway] will open up the natural beauty of Baltimore."

The idea behind dedicating transportation funds to trails for bikers and walkers is to encourage "multi-modal" travel -- such as biking to catch the train and light rail, said city environmental planner Beth Strommen.

Over the next decade, she said, the Jones Falls greenway will be the city's link to a continuous East Coast greenway from Maine to Florida.

In a confluence of volunteers, nonprofit networks and good intentions, the Jones Falls has received more attention lately than it has since nearly a century ago -- when landscape architects Frederick Law Olmsted Jr. and John Charles Olmsted mapped it out as a natural asset which links city neighborhoods.

Michael Beer, a retired Hopkins professor of biophysics, and Charles Smith 35, of the Midtown Community Benefits District were among those who helped create the festival that has taken six months to plan. The nonprofit organizations include the Parks and People Foundation and the Greater Homewood Community Corporation.

Beer, 72, born in Hungary and raised on a farm in Canada, has organized monthly volunteer Jones Falls cleanups since January. He says it's all been for a larger purpose: making people see the falls as a recreation area.

Some big objects had to be cleared out of view. "You don't see sofas and refrigerators," said Beer. "You can see the difference."

He is ready to move on to the next phase, marked by the festival. "Just cleaning it up is not enough," said Beer. "We have to change people's thinking. A river ought to be a source of delight as in San Antonio," which has a River Walk cutting through the city's center.

He described himself as "intrigued by the possibilities" of rock climbing and canoeing along Jones Falls.

Smith said that when he read the original Olmsted plan, he realized it showed how recreational space could be opened to inner-city children, who, he said, are often "left out" when it comes to park and playing space.

When the JFX opens to the public Sunday for walking and smog-free transportation, he plans to kick into action with his own private celebration. Said Smith: "I will be the first one blading down the highway."